It seems that the glittering caverns originally gave their name to the entire defensive complex, and there are records of the fortress that guarded the deep being called 'Aglarond' during the time it was still under Gondorian control. With the coming of the Rohirrim, these names were changed. Eventually the fortress became known as the Hornburg, and after that time the name Aglarond came to be used simply for the caverns from which it had originally derived.

Notes

1

The source of the Deeping-stream is not described in detail, but the fact that it ran out through the ravine that emerged from the caves, and that the caves were filled with 'an everlasting music of water' (ibid) it is hard to reach any other conclusion than that the stream emerged from Aglarond.